The invention relates to a rotating arc circuit breaker having a sealed enclosure filled with a high dielectric strength gas, notably sulphur hexafluoride, and housing one or more pole-units, each pole-unit comprising:
an extinguishing chamber having a pair of arcing contacts capable of defining a breaking gap when they separate,
magnetic blow-out means, notably a coil, or a permanent magnet designed to create a magnetic arc rotation field, causing the gas to be driven by a centrifugal effect towards the periphery of the chamber,
an annular arc migration electrode,
guiding fins located in the extinguishing chamber to slow down the rotation movement of the extinguishing gas.
In a rotating arc circuit breaker the centrifugal effect driving the gas towards the periphery of the chamber is capable of creating a depression in the vicinity of the breaking gap. This depression gives rise to a decrease of the gas density which weakens the dielectric withstand in this region. The speed of rotation of the arc is moreover close to the gas driving speed, which prevents any efficient heat exchange between the arc and the gas. This results in an insufficiency of the arc recovery voltage which may prevent the arc from being extinguished when short-circuit currents are broken.
The document FR 2,554,274 describes a rotating arc self-extinguishing expansion circuit breaker having guiding fins located in the extinguishing chamber to slow down the rotation movement of the extinguishing gas heated by the arc to the outflow zone. The fins are fixed on an insulating ring covering the arc migration electrode, i.e. in a region close to the breaking gap. A mixture of hot and cold gases takes place in a zone located away from the breaking gap. Arranging the fins in this way is liable to decrease the performances of the circuit breaker.
The object of the invention consists in improving the dielectric withstand, and the arc recovery voltage in a rotating arc circuit breaker.